CDP

Cisco Discovery Protocol is a Layer 2 protocol to discover directly-connected Cisco devices
- CDP messages are not forwarded to other devices
Enabled by default on most Cisco equipment
It is a closed-protocol similar to LLDP, but provides additional information on VLAN Trunking Protocol VTP
Messages are sent periodically to Multicast Address 0100.0ccc.cccc
Sends advertisements every 60 seconds by default, compared to LLDP's 30 seconds
- If a message isn't received from a neighbor within 180 seconds (CDP hold time), the neighbor is removed from the CDP neighbor table
CDP is enabled and configured globally, but can also be enabled per interface

sho cdp
1. Shows CDP timer
2. CDP hold time
3. Which version is enabled
show cdp traffic
1. Packets sent and received, and their version
show cdp interface
1. Information about all interfaces
show cdp neighbors
1. Shows host name
2. local interface (not the neighbor)
3. hold time
4. Capability (basically what kind of device)
  1. R = routing
    1. A layer 3 switch will have "R" as a capability
  2. S = switching
5. Platform
  1. Device model number
6. Neighbor port ID
show cdp neighbors detail
1. Software version
2. Interfaces
  1. "Interface" is the local interface
  2. "Port ID (Outgoing Port)" is the NEIGHBOR interface
3. VTP information
4. IP address
show cdp entry <device name, e.g. R2>
1. Same as neighbors detail, but for a specific entry

config# <no> cdp run
1. Run/Disable CDP globally
config-if# <no> cdp enable
1. Enable/disable CDP on an interface
`config# cdp <timer, holdtime, advertise-v2>
1. Modify the timer, hold time, or version

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